In a controlled thermodynamic test, a pure substance in a solid state is placed in a sealed piston-cylinder device and subjected to a steady, constant input of thermal energy until it becomes a superheated gas. Arrange the following molecular behaviors and thermal observations in the correct chronological order as the total enthalpy of the system increases.
- 1Molecules vibrate more vigorously within a fixed lattice, steadily increasing the substance's temperature.
- 2Temperature plateaus completely while thermal energy is absorbed as latent heat of fusion to break rigid intermolecular bonds.
- 3Fluid molecules flow freely past one another while the substance's temperature steadily rises.
- 4Temperature plateaus a second time while energy acts as latent heat of vaporization to overcome remaining molecular attraction.
- 5Molecules expand randomly to fill the cylinder volume, with temperature increasing rapidly as translational velocity maximizes.
Answer
The correct chronological sequence corresponds to the standard heating curve: sensible heating of the solid, latent heat of fusion (melting), sensible heating of the liquid, latent heat of vaporization (boiling), and sensible heating of the gas.
The correct sequence maps perfectly to the five distinct segments of a standard thermodynamic heating curve. Initially, the solid undergoes sensible heating (kinetic energy increases). Upon reaching the melting point, the temperature plateaus as latent heat of fusion breaks the lattice. Next, the resulting liquid undergoes sensible heating until it reaches its boiling point. A second plateau occurs as latent heat of vaporization separates the molecules entirely. Finally, the completely gaseous substance undergoes sensible heating, increasing its temperature further.
Step-by-Step Solution
Key Concept
During continuous heating, a substance alternates between sensible heating (where kinetic energy and temperature increase) and latent heating (where temperature plateaus because thermal energy is used to break intermolecular bonds during phase changes).